The present invention relates to an EPROM memory matrix made up of symmetrical elementary MOS cells as well as a writing method for said memory.
Conventional EPROM (Electrically Programmable Read-Only Memory) memories made with symmetrical elementary MOS (Metal Oxide Semiconductor) cells are known to call for the constitution of pairs of control gate lines superimposed on and self-aligned with floating gate areas spaced by parallel source lines connected to earth while drain contacts are interposed between one gate line and the next of each pair and connected electrically to metallization lines perpendicular to the gate and source lines. Field oxide areas are formed between the gate lines and an underlying silicon substrate to mutually insulate the elementary cells of the matrix.
The limitation of the memory made with this technology is dimensional, i.e. it is not possible to fall below certain minimal dimensions, primarily because of the tolerances between the gate lines and source lines, the distances between the gate lines and the drain contacts, and the side dimensions of the individual cells.